As a twin clutch type transmission with eight forward speeds, one described in Patent Document 1 below is known. This transmission has a small number of components and is compact, but since making the proportions between gear position ratios basically uniform cannot be avoided, there is the problem that there is no degree of freedom in setting ratios that achieve a balance between gear shift performance when starting and fuel economy when traveling at high speed. As another embodiment, one in which two supplementary sets of gears that are thought to be for ratio adjustment are added is disclosed, but because of this the overall length of the transmission increases and, moreover, there is the problem that the ratios of a first speed gear position and an eighth speed gear position cannot be adjusted independently. Moreover, since there are two more gears meshing at the highest speed position for all of those described in Patent Document 1, there is the problem that it is disadvantageous in terms of improving fuel economy, which is the original purpose of having multiple stages.
Furthermore, Patent Document 2 below proposes a transmission in which the number of gears meshing at the highest speed position is decreased, but since this has a large number of components, the overall length increases, and there is the problem that it is difficult to reduce the weight and make it compact.
Moreover, in the other embodiment of Patent Document 1 and one of Patent Document 2, since a universal joint mechanism provided on one of a main shaft and a countershaft and a drive gear provided on the other are disposed adjacently, in order to avoid interference therebetween it is necessary to either increase the distance between the two shafts or increase the axial dimension, and there is the problem that it becomes more difficult to reduce the weight and make the transmission compact.    Patent Document 1: Japanese Patent No. 3733893    Patent Document 2: Japanese Patent Application Laid-open No. 2007-225040